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Other Names: EFV, DMP-266, Sustiva®
Manufacturer: Bristol-Myers Squibb

What is it?

Efavirenz is an antiretroviral medication, specifically a non-nucleoside reverse transcriptase inhibitor. It is used to treat HIV, a retrovirus. Retroviruses use the genetic material in the body’s cells to produce more virus which can infect other cells.

How does it work?

Efavirenz interferes with the life cycle of HIV to stop it from producing more virus. Specifically, efavirenz ties up the reverse transcriptase enzyme so it cannot build the genetic material needed to make more virus and infect more cells.

How do I take it?

  • Efavirenz is available as 50mg, 100 mg, 200 mg capsules, and 600mg tablets
  • The usual dose is 600 mg once daily at bedtime.
  • It is recommended that efavirenz be taken on an empty stomach. (see Special Considerations).
  • While taking efavirenz, it is best to limit your consumption of alcoholic beverages.

It is extremely important that you take efavirenz and your other antiretroviral medications exactly as directed. You should set up a system that will help you remember to take your medicines so that you do not miss any doses. If you miss a dose, take it as soon as possible; however, if you skip a dose, do not take two doses at once. Do not stop taking the medication for any reason at any time unless you are directed to do so by your study clinician. If you are unable to continue taking your medication due to side effects, you should contact your study clinician immediately.

Special Considerations

  • Efavirenz should be stored at controlled room temperature in a dry place, out of the reach of children.
  • Taking efavirenz with food may increase the amount of drug in the bloodstream; this may lead to more frequent or more severe side effects.
  • Please bring your medication bottles (empty and partially used) to each study visit.

Pregnancy Risks

Efavirenz has been shown to cause birth defects in monkey fetuses/infants. Therefore, woman of childbearing potential must use a reliable barrier contraceptive (condom) while taking efavirenz. The effect of efavirenz upon birth control pills is unknown and birth control pills may not be effective in preventing pregnancy. If you become pregnant while taking efavirenz, inform your study clinician immediately.


Some drugs taken together may have interactions that cause illness or impair the effectiveness of the drugs. It is a good idea to always check with your study clinician before taking any other medications, prescription or otherwise, to be sure it will not interact with efavirenz.

The following medications should not be given together with efavirenz:

  • Astemizole (Hismanal®) St. Johns Wort (Hypericum perforatum)
  • Cisapride (Propulsid®)
  • Ergot derivatives (ergotamine or dihydroergotamine)
  • Midazolam (Versed®)
  • Triazolam (Halcion®)

The following medications may be given with efavirenz, but dosing changes may be required:

  • Amprenavir (Agenerase®)
  • Anticonvulsants (phenytoin, phenobarbital, carbamazepine)
  • Clarithromycin (Biaxin®)
  • Indinavir (Crixivan®)
  • Rifabutin
  • Rifampin
  • Saquinavir (Fortovase®)
  • Warfarin (Coumadin®)

Side Effects

Not everyone experiences side effects. When they do occur, they may be mild, moderate or severe. Some side effects cannot be felt by the patient but can be found through laboratory tests, so it is important to see your study clinician regularly for checkups so that side effects can be detected early and treated.

During the first weeks of therapy with efavirenz, the most common side effects of efavirenz are dizziness, drowsiness or insomnia, impaired concentration, and abnormal dreams. Other possible side effects of efavirenz include skin rash, headache, nausea or vomiting, depression, and changes in liver function tests. If these side effects occur and are severe, last for more than a few days, or seem to be getting worse, you should report them to your study clinician.

Do not stop taking efavirenz if you experience a mild rash without any other symptoms. However, it is important to immediately notify your study clinician that you have a rash.

If you experience a severe rash or a rash accompanied by a fever, blisters in your mouth, swelling, muscle or joint aches, you should call your clinician immediately. A serious reaction known as Stevens-Johnson Syndrome can occur with efavirenz.


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